One way in which camera shutters are activated is by the use of electromagnetic devices, known as actuators. Typically, the actuator includes a permanent magnet and a device for electromagnetically producing a magnetic field, such as an armature, which is a core/coil combination which produces a magnetic field when current is applied to the coil. The actuator is operably configured by positioning the permanent magnet relative to the armature to allow the magnetic field produced by the permanent magnet to be coupled with the magnetic field produced by the armature when current is applied to the armature. In some cases, the permanent magnet is movable relative to the armature. In other cases, the armature is movable relative to the permanent magnet.
When magnetic field coupling occurs, a disequilibrium in the magnetic alignment of the permanent magnet and armature results, thereby causing the actuator's movable part, either the permanent magnet or the armature, to move to a position where the permanent magnet's magnetic field is in an alignment with the magnetic field produced by the armature. Typically, the camera shutter is operably attached to the actuator's moveable part. Thus, when current is applied to the armature's coil, and a magnetic field is produced by the armature, the resulting movement of the actuator's moveable part causes the shutter device to be activated.
For example, U.S. Pat. No. 5,173,728 by SanGregory et al, assigned to Eastman Kodak Company, issued Dec. 22, 1992, discloses a magnet and shutter assembly for an electromagnetic shutter. Specifically, the magnet and shutter assembly disclosed includes a cylindrical magnet, a shutter blade connected to the cylindrical magnet and an armature, which includes a core/coil and air gaps in the armature. The cylindrical magnet is positioned in the armature's air gap and the magnetic field produced by the cylindrical magnet is coupled with the magnetic field produced in the air gap in the armature when current is applied to the coil. As a result of the disequilibrium caused by the coupling, the cylindrical permanent magnet rotates on a fixed axis within the gap of the armature in a direction which will magnetically align the cylindrical magnetic with the magnetic field produced by the armature when current is applied to the armature's coil. The rotation of the cylindrical magnet causes the shutter blade connected to the cylindrical magnet to move, thereby causing alignment of an aperture on the shutter blade and the camera's aperture.
One disadvantage of known electromagnetic devices is the inability to make use of relatively strong magnetic material because of the manufacturing expense associated with shaping such relatively strong magnetic material. For example, the permanent magnet disclosed in U.S. Pat. No. 5,173,728 is shaped cylindrically and includes a center hole, a lug and a bearing pin for alignment and attachment of the shutter blade to the permanent magnet and engagement with the bearing. Further, the lug is used to orient the north and south poles of the permanent magnet. In order to economically shape a magnet which includes alignment and orientation features, magnetic material which can be molded or pressed into shape is used. Magnetic material having relatively strong magnetic properties, such as sintered neodymium iron boron, cannot be molded or pressed into small, individual parts due to process limitations. As a consequence, such relatively strong magnetic material must be machined, which increases the manufacturing expense.
The inability to use magnetic material having relatively strong magnetic properties also creates torque, size and inertia disadvantages associated with known electromagnetic devices. Specifically, the rotation of the actuator's permanent magnet creates a torque which is transmitted to the camera shutter to activate the shutter. The stronger the magnetic properties of the permanent magnet, the greater the torque properties of the device. However, as stated above, in order to economically shape magnets with orientation and alignment features, magnetic material which can be shaped or molded is used. Such magnetic material has weakened magnetic properties. As a result, the torque properties of known electromagnetic devices are not as strong as they could be. Further, the use of relatively weak magnetic material requires the use of relatively more magnetic material to increase the torque properties of the device, thus creating size disadvantages. Moreover, the weight of the permanent magnet also increases as a result of the use of relatively more magnetic material, thus creating inertia disadvantages.
It would be desirable to provide an assembly which uses permanent magnets having relatively strong magnetic properties which can also be manufactured economically. It would be desirable to provide an electromagnetic actuator having reduced size and having improved torque and reduced inertia properties. It would be desirable to provide an assembly for an electromagnetic actuator which uses magnets which are of simple shape and that can be easily cut from larger stock having preoriented north and south poles. It would be desirable to provide a rotor for an electromagnetic actuator which holds simple shaped magnets in a fixed position relative to a drive arm and which can be economically and reliably manufactured.